WASHINGTON (CNN) -- U.S. Defense Secretary Robert Gates said Friday that he is confident the United States will have fewer troops in Iraq next year.

U.S. Defense Secretary Robert Gates testifies Thursday before the Senate Armed Services Committee.

"I'm not saying when in 2009, but I believe we will have a lower number of troops in Iraq in 2009," he said.

Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, spoke to reporters at the Pentagon after a week in which lawmakers grilled the two of them, Gen. David Petraeus, the top U.S. general in Iraq, and Ryan Crocker, U.S. ambassador in Iraq, about the situation in the war-torn country.

President Bush said Thursday he had no plans to reduce the number of U.S. troops in Iraq below 140,000 once they fall to that level this summer.

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He insisted everyone is "on the same page" about drawdowns. Asked if they are on the "same place on the same page," he drew laughter with his response, "Same line, same word."

Gates reiterated his hope that NATO will provide more troops for Afghanistan, where he and Mullen have said U.S. forces are stretched too thin.

He said a recent NATO summit in Bucharest, Romania -- at which France agreed to send a battalion of troops to Afghanistan -- had been encouraging.

"I think the fact that ... all of the NATO leaders unanimously endorsed being in Afghanistan and winning in Afghanistan is a big deal," the defense chief said.

"The fact is that virtually -- that most of the terrorist attacks that have taken place in Europe, and many of those that have been thwarted, have either been originated in Afghanistan or in [Pakistan's tribal areas], or they were trained there, or they were inspired from there. And so the Europeans need to understand there is a direct threat to their security."

Gates also confirmed the United States wants to continue working with Shiite cleric Muqtada al-Sadr, who commands the loyalty of the largest Iraqi militia, the Mehdi Army.

"He is a significant political figure. ... We want him to work within the political process in Iraq. He has a large following. And I think it's important that he become a part of the process if he isn't already," Gates said.

He denied the United States wants to arrest al-Sadr, whose forces mostly have operated under a cease-fire the cleric issued seven months ago. Al-Sadr threatened this week to end the truce but has not done so.E-mail to a friend